The present invention relates, in general, to a valve drive for an internal combustion engine, and more particularly, to a hydraulic clearance compensation element for a valve drive.
German patent publication DE-OS 14 25 653 describes a clearance compensation element for a valve drive of an internal combustion engine, with the clearance compensation element being acted upon by a cam of a camshaft. The clearance compensation element includes a hollow-cylindrical casing which defines an interior bore for accommodating a pressure piston, whereby the casing and the pressure piston are axially movable relative to one another. The bottom of the casing rests upon a gas exchange valve and defines together with a confronting end of the pressure piston a high-pressure chamber for hydraulic fluid. A check valve is positioned at the end face of the pressure piston to regulate a passage to the high-pressure chamber from a reservoir enclosed by the pressure piston. Formed between the bore of the casing and an outer surface area of the pressure piston is a leakage gap for hydraulic fluid, whereby at least in the zone of the leakage gap, the casing has a coefficient of thermal expansion which is smaller than the coefficient of thermal expansion of the pressure piston. A drawback of this conventional valve drive with clearance compensation element is its inability to compensate for rapid dimensional changes in the gas exchange valve, for example, when a large amount of heat is generated following a cold start.